Prior art hologram readers have depended on the use of holograms having a special format or special characteristics. Examples of prior art hologram readers are illustrated in FIGS. 1a and 1b. In the hologram reader of FIG. 1a, a holographic bar code is illuminated by a laser beam 520 that is generated by a laser 525. A pattern of spots 505 is then reconstructed onto a set of photodetectors 500 positioned specifically to detect spots at particular positions.
In the hologram reader of FIG. 1b, a hologram 510 containing a non-focused image recording is illuminated by a laser beam 520 that is generated by a laser 525. The laser beam 520 is incident at its reference (or conjugate reference) angle to reconstruct an image 555 onto a ground glass screen 550, where it can be seen by a human observer 560.
Another type of prior art hologram reader (not shown) does not actually read a hologram but instead compares a wavefront recorded in a hologram to a reference wavefront. Yet another type of prior art hologram reader (not shown) simply compares a single 2-D view of the hologram to a stored 2-D reference image.
U.S. Pat. No. 4,641,017 to Lopata, entitled Fraud Resistant Credit Card System
U.S. Pat. No. 5,331,443 to Stanisci, entitled Laser Engraved Verification Hologram And Associated Methods
U.S. Pat. No. 4,761,543 to Hayden et al., entitled, Holographic Security Devices And Systems
U.S. Pat. No. 4,108,367 to Hannan, entitled Token And Reader For Vending Machines
U.S. Pat. No. 5,712,731 to Drinkwater et al., entitled Security Device For Security Documents Such As Bank Notes And Credit Cards
U.S. Pat. No. 5,306,899 to Marom, et al., entitled Authentication System For An Item Having A Holographic Display Using A Holographic Record
U.S. Pat. No. 4,131,337 to Moraw, et al., entitled Comparison Reader For Holographic Identification Cards
U.S. Pat. No. 3,905,019 to Aoki, et al., entitled Pattern Recognizing Optical Apparatus
U.S. Pat. No. 5,666,417 to Liang, et al., entitled Fluorescence Authentication Reader With Coaxial Optics
U.S. Pat. No. 5,465,243 to Boardman, et al., entitled Optical Recorder And Reader Of Data On Light Sensitive Media
U.S. Pat. No. RE 035,117 to Rando, et al., entitled Scanner With Coupon Validation.
The prior art hologram readers described above and in the above-listed patents are capable of reading holograms only if the holograms are specially adapted for the reader. There is therefore a need for a hologram reader that is capable of reading all kinds of holograms without the need for the holograms to be specially adapted for the reader and is capable of reading variable information from holograms.